This invention relates to deflection instruments and their use for the measurement of various kinds of forces; in particular, it relates to an improved method and means for the continuous monitoring and recording of the phenomena measured by such instruments. In certain respects, this application is similar to a former publication, U.S. Pat. No. 2,986,697. However, it contains substantial improvements and innovations beyond those described in the earlier patent.
In many deflection instruments, the forces deflecting the movable element are subject to a field of force of one kind or another: where the relationship between the field and the forces or between the forces themselves are known, measurements may be undertaken. For example, when an electrostatic field of force controls the movement of a member that is collecting an electric charge, an electric current may be measured. Known physical laws relate the average current and the rate of deflection of the movable element.
More in particular, it is often desirable to use a quartz fiber electrometer in conjunction with an ionization chamber for radiation measurements. A well-designed electrometer is sufficiently accurate to be employed as a secondary standard but requires operator observation of the rate of deflection of the electrometer needle. The need for continuous operator attention has inhibited use of an electrometer for routine measurements despite its many desirable characteristics.
It is therefore an object of this invention to provide an improved method for the automatic monitoring of the phenomena measured by such deflection instruments.
It is also the object of this invention to provide other types of deflection instruments which are useful in various manufacturing, production or controlled process operations. These new types of deflection instruments have similar properties to the automatically operated electrometer which will first be described.
The electrometer is a deflection instrument having a movable element in an electric field of force. Since the field is electric the forces will be produced by electric charges (of opposite sign) supplied to the moving element. Also, associated with this instrument is a source of illumination and an optical system adjusted to focus the real image of the deflection element (usually provided in the form of a needle clamped at one end and free to vibrate at the other) upon an optical mask having one slit thereon. A photoelectric cell is either mounted behind the slit or is connected to the slit by means of fiber optics so that signals may be generated when the deflection element is in a null condition. The signals generated through the instrumentality of the real-image-optical-slit-photocell arrangement are then employed both to operate a feedback control for the instrument itself, as well as to control digital time counters and recorders, thus to store in memory digital information of the rate of change of the potential of the needle due to the charge accumulating thereon.
In employing such a unit of invention in connection with an ion chamber and a quartz fiber needle electrometer for the measurement of radiation, the "rate of charge" or "drift" method is employed and currents of less than about 10.sup.-16 ampere may be measured.
For the instruments of this invention, time is the dependent variable and is the principal quantity under measurement. Independent variables, such as voltage may be set by control knobs or are variables to be measured, as is the electric current with quartz fiber electrometers. Constants are either built into the instruments or are set by controls. As a result, all measurements appear as digital, time-interval readings. This makes it natural for the employ of microprocessor and microcomputer techniques so that the time interval readings may be immediately outputted to random access buffer memory for computation and control.
The arrangement provides for fully automatic operation of the scaler or digitizer. As a digitizer the instrument makes possible the change of information from analog to digital form. Another important object of the invention is to describe an automatic method of taking current measurements with an electrometer on a continuous basis. All measurements, it is noted, may be referenced to real time.
A further object of this invention is to apply this digitizing, flux-measuring equipment to the control of a nuclear reactor. Not only does such a digitizer afford a means of obtaining reactor flux levels at several places simultaneously in the core lattice, and at frequent, almost continuous intervals, but the readings may be further employed to obtain automatic control of the reactor's power output.
Another object of this invention is to employ rotating or deflecting arm instruments as optical, analog-to-digital converters. In such instruments, the real image of the deflecting arm may be used to derive time-interval measurements by means of an optical-slit, phototransducer system; or the moving arm itself may cause the diminution of optical flux incident upon the optical-slit, phototransducer arrangement.